Effects of boron on leaf chlorophyll fluorescence of greenhouse tomato grown with saline water

Imaging chlorophyll fluorescence was used to study the response of greenhouse tomato grown in soilless culture to NaCl and B concentration in the irrigation water. The plants were grown in perlite with recycling nutrient solution, which was prepared with negligible concentration or 550 mg L−1 of NaCl, and 0.5 or 2.0 mg L−1 of B in the irrigation water. High B concentration resulted in evident necrosis of leaf margins. At high NaCl concentration the recycling nutrient solution was replaced more frequently than at low salinity and this resulted in lower B concentration in the root zone, thus limiting the incidence of necrotic areas in the leaves. Indeed, the severity of leaf damage was linearly related to the mean B concentration in the recycling water. In all treatments we observed a strong difference in B concentrations between marginal and central areas, the latter remaining green and viable even in condition of severe B toxicity, as indicated by the determination of chlorophyll fluorescence. A reduction of the photosynthetic activity was observed in the symptomatic areas of the leaves on the plants grown at high B concentration in the root zone as a result of reduced dissipation of the excess of excitation energy at PSII level.

Research highlights▶ The range between concentrations of B essential for growth and leading to toxicity is narrow. ▶ High B concentration resulted in evident necrosis of leaf margins. ▶ At high NaCl the incidence of necrotic areas B-induced diminished. ▶ A reduction of photosynthetic activity was observed in the symptomatic areas.